This invention relates to methods of biologically degrading halogenated hydrocarbons including trichlorethylene (TCE).
Halogenated hydrocarbon compounds are high-volume products of the chemical process industry; for example, more than 6 million metric tons of trichloroethylene (TCE), tetrachloroethylene (PCE), trichloromethane, carbon tetrachloride (CT), and chloroform (CF) are produced each year. Those halogenated hydrocarbon compounds most frequently found in groundwater are low molecular weight aliphatic halogenated hydrocarbons: TCE, dichloroethane (DCA), trichloromethane, and PCE. Many of these aliphatic halogeated hydrocarbon compounds, including TCE, have been listed as priority pollutants by the U.S. Environmental Protection Agency, and are known or suspected carcinogens and mutagens. Haloforms (halogenated derivatives of methane) are also frequently detected in groundwaters and drinking waters. Some haloforms are produced during chlorination of water supplies, but inadequate disposal techniques or accidental spillage may also be responsible for the release of these haloforms.
Several of the halogenated hydrocarbon compounds mentioned above are resistant to biodegradation in aerobic subsurface environments, or their biological transformations are incomplete under anaerobic conditions. For example, under anaerobic conditions, TCE and PCE are known to undergo partial bioconversion to vinyl chloride, a compound which is as much or more of a problem as the original contaminants. Wilson and Wilson, Appl. Env. Microbiol., 49:242-243 (1985).
Current technology for reclaiming groundwater polluted with these halogenated hydrocarbon compounds involves pumping water to the surface and stripping out the contaminants in aeration towers, or removing the pollutants on a sorbent. The former process is not permitted in some states, and the latter is expensive and involves the production of concentrated toxic materials that may present future problems.
A number of methanotrophic bacteria have been shown to degrade TCE. Little et al., Appl. Envt. Microbiol. 54: 951-956 (1989); Wackett and Gibson, Appl. Envt. Microbiol. 54: 1703-1708 (1988). However, to date degradation of TCE by chemo-litho-autotrophic bacteria has not been reported. In view of the environmental problems associated with halogenated hydrocarbons there is a need for a method to degrade halogenated hydrocarbons utilizing ammonia-oxidizing bacterium.